HPCC-9603 Add information into Language Guide under IN

Signed-off-by: RichardTaylorHPCC <richard.taylor@lexisnexis.com>

Rebased and fixed trailing whitespace issues

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge branch 'B9603' into candidate-4.0.0

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>